With the cable detached try how much they spring back when you apply the brake bike hand, this should tell you if the stickiness is in the brake arms or the cable. Additionally if you need more spring back tension the return spring locating pin may have more than one position on the fork mount.

First try using the webupdater to see if it offers you a time zone map update if it does then take it.
If it does not then mount the Edge to the computer and delete the following file
Garmin\gmaptz.img (This is the time zone map)
Run the Webupdater after deleting the file and it will reinstall the map for you.

Adding glue does nothing to help the nutserts hold, if they are installed correctly.
The image is showiing stainless steel nutserts into stainless steel.
Bikes usually have aluminium ones as they are easier to set.
I have nutserts, setting tool and a 7.1mm drill if you fancy doing it yourself? 7.1 mm is the size for M5 nutserts. (rivnuts is an americanism).